This invention relates to a refrigerating apparatus which is provided with two coolers or evaporators and adopts a double-stage evaporation system.
In a single-stage compression type refrigerating apparatus including a compressor, a condenser, a pressure reducing means and a cooler (evaporator) connected to one another in the indicated order to form a refrigerating circuit through which refrigerant flows, the quality of the refrigerant at the inlet of the cooler increases when the evaporative temperature becomes low. Thus, the latent heat of evaporation which has the function of cooling is reduced in amount and the specific volume of the refrigerant, in a gaseous state drawn into the compressor, and compression ratio of the refrigerant by the compressor increase thereby decreasing the coefficient of performance.
In order to eliminate this disadvantage, a double-stage compression system is adopted when the evaporative temperature is below about -40.degree. C. to provide improvements in the quality of the refrigerant at the inlet of the cooler and the compression ratio. However, a single-stage compression system is still adopted for refrigerating apparatus wherein the evaporative temperature is about -40.degree. C. or over -40.degree. C.
In single-stage compression type refrigerating apparatus used in this temperature range, a refrigerating apparatus of the double-stage evaporation system provided with a deep-freeze compartment and a cold storage compartment is known which includes two coolers (evaporators) of different evaporating temperatures.
A two-temperature type refrigerating apparatus, as described in the specification and shown in FIG. 2 of Japanese Utility Model Publication No. 26927/72, comprises a compressor, a condenser, a first pressure reducing means, a first cooler, a second pressure reducing means, and a second cooler connected in series with one another in the indicated order to provide a refrigerating circuit, wherein the refrigerant in the first cooler has a higher evaporative temperature than the refrigerant in the second cooler. This refrigerating circuit might be faced with the problem that difficulties are experienced in regulating the distribution of the refrigerant in a liquid state to the first cooler and the second cooler, so that the cooling ability of each cooler might become too large or too small to cope with a variation in cooling load. Another problem that might arise is that the suction pressure of the compressor is substantially as low as the pressure in the second cooler in spite of the pressure in the first cooler being high.